I'm from another nation-oriented instance that has an outsized presence, right next to Duitsland.

My guess is:

• Germany is a big, populated country
• People from DACH also gravitate towards feddit.de
• The culture kinda gives itself to the project
• The NL and the EU are the main funders of Lemmy
• The government itself is embracing the Fediverse

Generally internet culture In the Dach region is very active and forward looking, and potentially ideologically aligned with the idea of Fediverse and generally FOSS software and privacy. E.g. for Wikipedia language share German got overtaken by Spanish only within the last 5 years slipping from 2nd to 3rd suggesting some early adopter and internet participation higher than the norm.

Subjectively a lot of people here have uneasiness with big tech, and are relatively informed about alternatives.DACH on Reddit was also very big, and very ideologically opposed to API changes and general Reddit corpo behaviour. Subjectively again Dach and ich_iel felt like home when I joined, essentially like the Reddit culture I was used to, just with a little more progressive views across the board.

Also I suspect that German language speakers are fairly active within the English speaking parts of the internet in general, while Spanish and French as well as other non Germanic languages seem to have more disdain for English language content and sites, Germans and Dutch as well as Nordics are very comfortable with English as a common language.